This invention relates to a seat reclining apparatus for an automotive vehicle and more particularly to an improvement of a seat reclining apparatus in which an inclination angle of a seatback is adjusted by a so-called differential transmission mechanism in which an inner gear partly engaged with an outer gear having smaller number of teeth than the inner gear is relatively swingingly rotated by movement of the engagement parts of the inner and outer gears and which is capable of eliminating rattling of the seatback when the inclination of the seatback is fixed and smoothly conducting engagement transmission between the inner gear and the outer gear when the seatback is in the adjusting position.
Japanese Patent Publication No. S63-47443 discloses one example which employs the so-called differential transmission mechanism as means for adjusting the inclination angle of a seatback in a seat reclining apparatus for an automotive vehicle.
This related art includes a rotation shaft (swinging shaft) which supports thereon one of an inner gear and an outer gear, and an eccentric shaft part (eccentric ring) which supports the other gear. The eccentric shaft part, which supports thereon one of the inner and our gears, comprises, in a space between an inner hole of this gear and the rotation shaft, a disc (interlocking disc) integral with the rotation shaft, two wedge pieces having tapered end parts which are arranged in opposite directions, and a spring interposed between opposing wide end parts of the two wedge pieces and for biasing the two wedge pieces in the pushing away directions. Moreover, those components are arranged on a same plane which is orthogonal to the rotation shaft.
In a state where the seatback is fixed at a desired angular position, the mutually oppositely directing wedge pieces are biased by the spring in a direction sandwichingly inserted and bitten between the circumferential range (area surrounding the rotation shaft) of the disc and the circumferential range of the inner hole of the gear. Thereby, the center of the rotation shaft and the center of the eccentric shaft part are brought away from each other (the amount of eccentricity is increased) and the inner gear and the outer gear are press contacted with each other at the engaging parts thereof. By this, rattling of the seatback caused by so-called engagement play is eliminated. At the time of adjustment of inclination of the seatback, a projection (interlocking projection) of the disc which rotates together with the rotation shaft, is abutted with the tapered end of the wedge piece to push the wedge piece against the biasing force of the spring. By this, the sandwichingly inserted and bitten state in the position fixed state is released to release the press contacted state at the engaging parts. Thus, the inner gear and the outer gear are brought into a smooth engagement transmission state. As a result, the inclination adjustment is made by relative swinging rotation between the inner gear and the outer gear caused by rotation of the rotation shaft and the eccentric shaft part.
As a technique related to the above-mentioned art, there is a technique disclosed by Official Gazette of Japanese Patent No. 2756516.
In the inclination angle adjustment means for an automotive vehicle seat by such a differential transmission mechanism, the smooth rotation transmission of the inner and outer gears is desirous for the adjustment of inclination of the seatback. For this purpose, the inner gear and the outer gear are engaged with each other through backlash (play between mutually engaging gears, hereinafter referred to as xe2x80x9cengagement playxe2x80x9d).
However, this results in such inconveniences that in the desired inclination position (position fixed time) after adjustment, the backseat is vibrated caused by the above-mentioned engagement play. For this reason along with the manufacturing tolerance (hereinafter referred to as bearing space) of the supporting part of each gear, the seatback is heavily rattled, thereby giving an unpleasant feel to the person who sits on the vehicle seat. Moreover, this rattling is amplified when the shock is applied to the vehicle seat, thereby applying a significant adverse effect to the vehicle seat.
The above-mentioned related art (Japanese Patent Publication No. S63-47443) aims at solving the above inconveniences. It is designed such that a disc forming an eccentric shaft part as its main part, two wedge pieces and a spring are arranged on a same plane which is orthogonal to the rotation shaft.
This disc is, however, required to have a sufficiently large strength because it releases the sandwichingly inserting and biting action of the wedge pieces during the time the disc rotates together with the rotation shaft and pushes and rotates the wedge pieces so that the eccentric shaft part is brought into a rotating state to allow the rotation of the gears which are supported thereon. Since the disc occupies an arcuate angle range having a wide angle on the same plane which is orthogonal to the rotation shaft, one wedge piece takes an arcuate angle range having a narrow angle in consideration of a provision of the spring. Accordingly, it is in the form of a short piece defined by an arcuate inner side surface and an arcuate outer side surface in which one end is tapered and the other end is somewhat large in width.
In a state where the entire arcuate outer surface part of each wedge piece is in contact with the circumferential surface of the inner hole of the gear when the wedge piece is sandwichingly inserted and bitten when the seatback is in fixed position and the arcuate inner surface part is in contact at its one point with the disc outer peripheral surface (area surrounding the rotation shaft). Accordingly, since the load coming from the seatback is concentrated on the arcuate outer surface part having a narrow arcuate angle through one point of the arcuate inner surface part, there is a fear of escape of the wedge piece from the plane in the axial direction because of its arcuate short piece shape.
Moreover, when the seatback is in the fixed position, the sandwichingly inserting and biting action of the wedge piece is released, and the wedge piece is moved in accordance with rotation of the disc, thereby rotating the gear which is supported on this eccentric shaft part. However, the gear is rotated by sliding contact relation between the arcuate outer surface part of the wedge piece having a narrow arcuate angle and the circumferential surface of the inner hole of the gear while maintaining the amount of eccentricity between the rotation shaft part and the eccentric shaft part. Thus, along with the above-mentioned escape action caused by the load, unstableness is accompanied. In addition, since the amount of eccentricity is varied by the approaching/departing movement of the two wedge pieces caused by degree of expansion/contraction of the spring which is interposed between the two wedge pieces, proper engagement (backlash) between the outer gear and the inner gear is unobtainable, thus making it difficult to adjust the position of the seatback. Accordingly, those wedge pieces invite high surface pressure and increased degree of wear caused by load applicable within the narrow arcuate angle range when the seatback is in the fixed position and when the seatback is in the adjusting position, and by sliding contact. Thus, dynamic characteristics and durability are decreased. In order to obtain an adjustment mechanism having a large strength by overcoming those inconveniences, it is required that the various members including the wedge pieces are increased in precision and the entire apparatus is increased in size. This results in increase of the manufacturing process and various expenses.
As means for solving the inconveniences, there is known a device as disclosed in the above-mentioned Official Gazette of Japanese Patent No. 2756516.
This conventional device comprises a dick (engagement body) whose eccentric shaft part (eccentric part) is integral with the rotation shaft (swinging shaft), a spring (biasing force accommodating device), two wedge pieces (wedge parts) and a crescent-shaped centering part disposed at an area in the vicinity of the wedge pieces. The eccentric shaft part is surrounded by an inner hole (support hole) of the outer gear (one joint part, spur gear with an outer gear).
When the seatback is in the fixed position (non-operated position), rattling (play in the radial direction) caused by the sandwichingly inserting and biting action of the two wedge pieces is eliminated in the same manner as mentioned above. When the seatback is in the adjusting position (during adjusting motion), the inner hole of the outer gear is supported by the centering part. As seen, the action (function) is shared. By making the outer periphery of the centering part slide into contact with the inner periphery of the inner hole over the wide arcuate angle range, low surface pressure and wearing resistance can be obtained.
However, since this conventional art requires an additional member of the centering part, the cost and the number of assembling processes are increased. In addition, in order to exhibit the above function, a high degree of precision is required for the centering part which is slid into contact with the area surrounding the rotation shaft and the inner hole of the outer gear over a wide angle range so as to hold the outer gear. Moreover, in actual practice, since even a small error in dimensional relation between the centering part and the wedge pieces can make an intended effect unobtainable, precision management of those component parts is difficult to perform. Thus, inconveniences may occur at the time of a machining process and an assembling process.
It is, therefore, an object of the present invention to provide a new technique usable in a seat reclining apparatus for an automotive vehicle, which technique is capable of eliminating rattling of the seatback, which would otherwise occur due to sandwiching insertion and biting and withdrawal of an eccentric part which constitutes an eccentric shaft part when the seatback is in a fixed position, and capable of performing a smooth rotational transmission between the outer gear and the inner gear, and which technique has favorable load resistance and wear resistance.
The features of the present invention reside in a seat reclining apparatus for an automotive vehicle in which an inclination angle of a seatback with respect to a seat cushion is adjusted by a differential transmission mechanism in which an inner gear and an outer gear having slightly smaller number of teeth than the inner gear are supported in their partly engaged states by a rotation shaft part and an eccentric shaft which is eccentric with respect to the rotation shaft, wherein the eccentric shaft part includes two wedge plates sandwichingly inserted between a bearing ring inner peripheral surface which corresponds to a center hole of the outer gear and a bearing cylinder outer peripheral surface of the inner gear when the seatback is in a fixed position, a spring rod for biasing the two wedge plates in opposite peripheral directions that are coincident with the sandwichingly inserting direction, and an operation piece part for releasing the sandwichingly inserting states of the wedge plates when the seatback is in the fixed position by being rotated together with the rotation shaft and rotated together with the wedge plates when the seatback is in an adjusting position, each of the wedge plates being in a generally crescent shape including an arcuate outer surface part which is slid into contact with the inner peripheral surface of the bearing ring and an arcuate inner surface part which is slid into contact with the outer peripheral surface of the bearing cylinder when the seatback is in an adjusting position, the two wedge plates being arranged in an overlapping relation in the axial direction of the rotation shaft. The wedge plates are each approximately 180 degrees, or 180 degrees or more in arcuate angle which is formed between the arcuate outer surface part and the arcuate inner surface part.